Antenna



May 8, 1956 o. NORGORDEN ANTENNA Filed Dec. 14, 1945 Illll POWER CIRCUITLII-51 gwuam too OSCAR NORGORDEN IOI United States Patent O ANTENNAOscar Norgorden, Washington, D. C.

Application December 14, 1945, Serial No. 635,117

7 Claims. (Cl. 343-834) (Granted under Title 35, U. s. Code 1952' sec.266) This invention relates to'antennas, and is particularly directed toproviding an antenna whose input impedance can be adjusted to match thesurge impedance of the transmission line to which it is connected.

Because radio apparatus can seldom be installed imrnediately adjacentthe input terminals of its associated antenna, almost every radioinstallation involves the use of a transmission line to interchangeenergy between the radio apparatus and the antenna. The termination ofsuch a line has a significant bearing on successful system operation.

Important advantages result from terminating a line in its surgeimpedance. When such a termination is effected, no standing waves arepresent on the line, and the input impedancetolthe line is a constant,equal to the surge impedance, regardless of the length of the line. Thepower transfer achieved by the line is, moreover, not sensitive to smallchanges in transmitter frequency, and the line operates with maximumefliciency and minimum losses. In view. of these advantages, terminationof. R. F. (radio frequency) lines in their surge impedances is, analmost universal practice. a

Practical R..'F. lines have as surge impedance aresistance, ranging fromperhaps fifty'ohms for coaxial lines to severalhun'dred ohms' foropen-wire lines, The impedance presentedby the input terminals of anantenna depends upon the physical conformation of. the antenna and uponthe character and location of .nearby objects. It is not necessarilya'pure resistance. 'Both the resistive and reactive components of inputimpedance for practical antennas may be anywhere within wide limits. Inconsequence, some type of impedance transformation apparatus hasheretofore been employed inradio 'systemsas a n'ieans of coupling anantenna to the line which is expected to transfer energy to or from it.

This invention eliminates the necessity for sneh coupling apparatusfitprovides an antenna whose input impedance may be adjusted within widelimitswithout materially affecting the, directional or radiatingproperties of' the antene na. Thus such an antenna may be adjustedtoaiford a surgeimpedance termination for the line without need forpedance transforming apparatus to couple the antenna to the line. Thisis accomplished by employing in combination a'driyen antenna and aparasitically excited antenna placed parallel andclosely adjacent thedrivenantenna'.

The separation between the antennas is very small in terms of wavelength; it may be of the order of one-fortieth wave length. By reason ofits proximity .to thedriven component, the parasitic component of theantenna does not appreciably alter the directive pattern possessed bythe principal component alone. By appropriate choice of lengths for suchan antenna, its input impedance may be madea resistance equal toany'desired value'within a wide range.

One of the objects of this invention to provide an antenna which may beadjusted to match the surge impeda ance of a transmission line withoutany impedance transformer.

2,745,102 firs May 8,

Another object of this invention is to provide an antenna comprising adriven component anda parasitically excited component in proximitythereto, having in combination a directional pattern similar to that ofthe driven component alone and having input impedance equal to the surgeimpedance of its associated transmission'line.

Detailed description of the invention will be with reference to theappended drawings, of which:

Figure l is a view, principally in cross section, of one embodiment ofthe invention comprising a vertical radiator and an artificial'groundplane, mounted at the top of a mast;

"Figure 2 is a perspective view of another embodiment of the inventionwherein a vertical radiator is associated with a reflector to effectdirectional radiation;

Figure 3 is a diagrammatic showing of an embodiment of the inventionutilizing a balanced center-fed dipole in conjunction with aclosely-spaced, parallel, parasitic antenna, designed to be operative infree space without a ground plane; and

Figure 4 is a diagrammatic representation of an embodiment of theinvention as it might be designed for low frequency applications. a

Figure 1 shows, primarily in cross section, the constructional detailsof an antenna mounted atop a hollow cylindrical mast, the antenna havingnon-directional characteristics in'the horizontal plane such as might beappropriate for beacon service or broadcasting. The radiating elementsc'onsistof vertical driven component 5 and parasitically excitedcomponent '6, parallel and closely adjacent. Both components work inconjunction with an artificial ground plane made of a plurality ofconducting rods 31, extending radially outward immediately beneath andin a plane perpendicular'to the axes of antenna compone'nts 5 and 6.Components 5 and 6 are cylindrical in shape and formed ofconducting-material.

v The supporting structure for the antenna assembly is hollow mast 7. Aheavy conducting sleeve 8, having an inwardly extending shoulder 9integrally formed with its upper portion, fits snugly over the top ofmast 7, the lower side of shoulder 9 resting, as shown, on the upper endof'the mast. A cap 10, fashioned of insulating material; is rigidlyafiixed to the upper end'of sleeve 8 by bolts 11 which extend through aplurality of formed open- .ings 12 circularly disposed in cap 10. Thesebolts are threaded into the upper part of sleeve 8. A gasket 23" beingidentical to'the axis of bolt 46. Hexagonal portion 14 affords a meansof tightening bolt 46, and it also serves as'a base for the lowerend ofantenna component 6,

which'snugly'engages' extension 13 when fitted thereon.

The inner side of the upper end of sleeve 8 is recessed to forma ledge15, which serves as a seat for the flanged upper end 16 of a chamberedstufiing box 17. Snufiing box 17 has formed within its flanged end acylindrical apertur'e ls of diameter such as to engage closely a coaxialtransmission line 19, which runs to the-antenna assembly through thehollow interior of mast 7. Thelower portion the cap10,- and ahollowmember 26'is fittedtherein.

The lower end of member 26 has a head substantially largerthan theaperture 25, and the upper end of member 26 is threaded to engage a nut27 which holds it firmly in. place. Central conductor 28 of coaxialline19 is inserted in hollow member 26 and is soldered-thereto. The upperend of member 26, as shown in the drawing, extends beyond the nut 27,providing a conductive support for the enlarged end of a machin'ed'plug29'having internal threads adapted to engage tightly the threaded end ofmember 26. The upper end portion 30 of plug 29is cylindrical and ismachined to effect a tight friction lit with antenna component 5.

Extending perpendicularly from the vertical edgeof sleeve 8 areaplurality of radially disposed rods 31 in-. serted and welded intosuitable openings 'in sleeve 3'. The' rods 31 provide an effectiveartificial ground plane for the antenna system.

Line 19 may be led, as shown-, from base 1 of mast 7 to a power circuit2, which may bea radio transmitter or receiver.

Initial determination of the proper lengths for antenna components 5 and6 in a particular application, may best be determined empirically byusing a transmitter and a section of slotted'coaxial line. Variouslengths for components 5 and 6 may then .be tried successively, thestanding wave ratio on the line being measured-for each set ofconditions. Correct adjustment will be indicated by unity standing waveratio on the transmission line. It will normally be found that formatching to a coaxial line the correct length for the driven componentwill be near a quarter, wave length-in some cases more and in some casesless--while the correct length for the parasiticallyexcited component isnormally somewhat less than a quarter wavelength.

In one specific construction. designed for operation at a frequency of246 me, a wavelength of 122 centimeters, 29 centimeters for the drivencomponent and 23 centimeters for the parasitic component were found tobe correct lengths for matchingto a line having surge impedance of 52ohms. In that embodiment rod of quarterinch diameter was used for theantenna components and the spacing, center to center, between thecomponentswas one inch, or 2.54 centimeters.

In another construction for use at 143 mc., a wavelength of 210centimeters, the lengths found to yield correct matching to a 52 ohmline Were 59 centimeters for the driven component and 47.3 cm. for the:parasitically excited component. used for the driven element and rodfor-the parasite. The spacing was one inch, center to-center. It hasbeen found that the spacing between. the components is not critical,solong as it is kept to a small fraction of a-wavelength-perhaps onefortieth wavelength or less. The. presence of the-parasitic: componentdoes not appreciablyafiect the directional pattern under suchcircumstances.-

Determinationof proper lengths for the components need not be made withthe system on. ahigh mast; if the antenna is matched to the line whenthe system is areasonable distance off the ground, the match will not beaffected by raising. the system to its normal opera-ting: position.

Figure 2 shows an embodiment of the invention as employed in adirectional antenna system. In this embodiment the system is mounted on.a verticalmast32 and is fed by a coaxial transmission line 36. Theradiating components of the system comprise adriven element 34 and aparasitically excited element 35-,mounted parallel and closely adjacent,as in the embodiment of Figure 1. They are mounted on head. 33 at thetop of mast 32. The details of the mounting and feed arrangements are.not shown in Figure 2; they. may be of the same general characteras inthe embodiment ofi Figure 1; A ground plane is formed by the pluralityof conduetingrods 41' which ex-tendradially outward from head 33.

In this embodimentdirective characteristicsare-imparted by a reflectorscreen 37, disposed in back of the dipoles and above the ground plane,consisting of a rigid conducting framework on which is mounted aplurality of vertical rods or wires 38. These vertical conductors 38 arespaced a small fraction of a wavelength apart and as a result functionas effectively as a closed screen to reflect radiation from dipoles .34and 35, while being lighter and OlTering less wind resistance than asolid refiector. The reflector assembly and the ground plane aremechanically reinforced by rigidbraces- 40 which converge to supportingring 39 on mast 32 below the antenna head 33. In the specific embodimentof Figure 2 the reflector is shown as a corner reflector.

Figure 3 shows diagrammatically an embodiment of the invention in whichthe driven and parasitic antenna components are designed to radiateindependently rather than in cooperation with ground or an artificialground plane. Transmission line 89, which may be of the open wire orcoaxial type, is connected to driven component 88; parasitically excitedcomponent 90 is placed parallel to' and closely adjacent component 88.As in the previously described embodiments, the lengths of components 88and- 90 are proportioned to effect an impedance match between line 89'and the input terminals to driven component 88.

If it were desired to employ the invention in a low frequencyapplication, adjustment by varyingthe lengths of the driven element andparasitic element might not be convenient, because of the physical sizeof the system. Accordingly for low frequencies an embodiment such asthat of Figure 4 would be appropriate. In Figure 4 transmission line 101feeds radiator 102, which is represented as a vertical radiator workingagainst ground and having a top loading system 106, which might consistof a network of horizontal wires. In series with radiator 102 at itsinput terminal is variable inductance coil 104, which serves as a tuningdevice. Adjacent and parallel.

- to radiator 1-02 is parasitic radiator 103, which also works againstground and'is top loaded by network 107. In" series with radiator 103near its grounded end is variable inductance coil 105,.which serves as atuning means for theparasitic element. The separation between thedrivenand parasiticelements is, as in the other embodiments, a

In that construction rod was very small fraction of a wavelength, sothat the presence of the parasitic element doesv not disturb thedirective pattern of the driven element. In this embodiment, adjustmentfor proper. operation should be accomplished in themanner. prescribedfor. the high frequency embodiments, except that the radiating elements102 and 103. should be tuned, by varying. the inductance of coils 104and 105, insteadof by varying the lengths of the elements.

It will be understood. that the embodiments of the invention hereinshown and described are exemplary only,

and that the scope of the invention is to be determined from'the'appended claims.

The inventionv described hereinv may be manufacturedandiusedby or forthe-Governmentof' the. United/States of America for governmental.purposes without the. payment of any royalties thereon or therefor.

What is claimed is:

1. An antenna having a. primary element, aground plane positioned atoneend of-"the. primary: element, a transmission line havinga uniform.impedance throughout connectedbetween the groundplane. andthe primaryelement,. a plurality. of rods connectedto said ground plane to providea reflector screenfor said primary. element and a. parasitic element ofa length less than said primary element and positioned alongside-theprimary element and'connected tothe ground planecperativeto effect aterminatingirnpedance for the transmission line equal to its surgeimpedance, the spacing between saidprimary element and. said. parasiticelement: being: sulficiently: small to preserve thedirectivity pattern'possessed by the primary; element alone.

2. An antenna assembly including a supporting/cap cap alongside theprimary element a distance less than a twentieth wavelength therefromand conductive rod means extended at right angles from the side of thecap connected to the outer conductor of the coaxial line and to theparasitic element, the conductive rod means providing a ground plane forthe primary element and the parasitic element, the parasitic elementbeing operative to effect a terminating impedance for the coaxial lineequal to its surge impedance, said spacing between said primary elementand said parasitic element being sufiiciently small to preserve thedirectivity pattern possessed by the primary element alone.

3. In combination an antenna having a primary element, a powerinterchange circuit, a transmission line connecting the primary elementto the power interchange circuit, and a parasitic element shorter thansaid primary element positioned closely adjacent to said primaryelement, the length of said parasitic element beingchosen to cause amatch between the input impedance of said primary element and the surgeimpedance of said line, and the spacing between said primary element andsaid parasitic element being sufiiciently small to preserve thedirectivity pattern possessed by the primary element alone.

4. In combination an antenna having a primary element approximately aquarter wavelength long at its operating frequency, a power interchangecircuit, a transmission line connecting the primary element to the powerinterchange circuit, and a parasitic element positioned adjacent to saidprimary element and of a length less than a quarter wavelength formatching the input impedance ofsaid primary element to the surgeimpedance of said line, the spacing between said primary element andsaid parasitic element being sufliciently small to preserve thedirectivity pattern possessed by the primary element alone.

5. A directive antenna comprising a supporting mast having a mountingpart positioned at its upper end, a coaxial transmission line havingauniform characteristic impedance throughout disposed within said mast,said mounting part providing means for connecting the outer conductor ofsaid line to said mast, a, radiating element having one end connected tosaid mounting part for support thereof, said mounting part alsoproviding means for connecting the inner conductor of said line to saidradiating element, a parasitic element paralleling said primary elementoperative to effect a terminating impedance for the coaxial line equalto its surge impedance, said parasitic element being electricallyconnected to said mounting part and mechanically supported thereon, thespacing between said primary element and said parasitic element beingsufficiently small to preserve the directivity pattern possessed by theprimary element alone, a plurality of conductive rods extending radiallyfrom said mounting part perpendicular to the longitudinal axis of saidelements to provide therefor a ground plane, and a plurality of verticalwires disposed above said rods and back of said elements to provide areflector screen therefor.

6. An antenna comprising a radiating element and a parasitic element,coaxial transmission line means for feeding said elements, a supportingmast for supporting said elements having a sleeve surrounding theuppermost portion of said mast, said sleeve having an integrally formedshoulder extending inwardly over the upper end of said mast, aninsulating cap extending over the upper end of said sleeve, a pluralityof means for rigidly fixing said cap to said sleeve one of said lastnamed means extending above said cap for engaging said parasiticelement, an aperture extending through the central portion of said cap,a conductive member extending through said aperture operative tosecurely engage said radiating member to said cap, means for connectingthe inner conductor of said transmission line to said conductive member,and means for connecting the outer conductor of said coaxialtransmission line to said sleeve.

7. An antenna comprising a radiating element and a parasitic element,coaxial transmission line means for feeding said elements, a supportingmast for supporting said elements having a sleeve surrounding theuppermost portion of said mast, said sleeve having an integrally formedshoulder extending inwardly over the upper end of said mast, aninsulating cap extending over the upper end of said sleeve, means forrigidly fixing said cap to said last named means extending above saidcap for engaging said parasitic element, an aperture extending throughthe central portion of saidcap, a conductive member extending throughsaid aperture operative to securely engage said radiating member to saidcap, means for connecting the inner conductor of said transmission lineto said conductive member; said shoulder of said sleeve having a recessat its upper end, a stuffing box having an outwardly flange seated insaid recess, a cylindrical aperture formed in the longitudinal axis ofsaid stuffing box extending through said flange, said outer conductor ofsaid transmission line extending through said aperture and engaging theinner wall of said stufling box, and means for securely fastening saidouter conductor to said flange.

References Cited in the file of this patent UNITED STATES PATENTS1,745,342 Yagi Jan. 28, 1930 1,860,123 Yagi May 24, 1932 1,934,412Englund NOV. 7, 1933 2,026,652 Ponte Jan. 7, 1936 2,274,149 Lubcke -2Feb. 24, 1942 2,275,342 Brown Mar. 3, 1942 2,476,949 Adams et al. July26, 1949

